// 32.最长有效括号

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

class Solution {
public:
    int longestValidParentheses(string s) {
        int res = 0;
        int n = s.length();
        vector<int> dp(n, 0);
        for (int i = 1; i < n; i++) {
            if (s[i] == ')') {
                if (s[i - 1] == '(') {
                    dp[i] = (i >= 2 ? dp[i - 2] : 0) + 2;
                }
                else if (i - dp[i - 1] > 0 && s[i - dp[i - 1] - 1] == '(') {
                    int pre = i - dp[i - 1] >= 2 ? dp[i - dp[i - 1] - 2] : 0;
                    dp[i] = pre + dp[i - 1] + 2;
                }
                res = max(res, dp[i]);
            }
        }
        return res;
    }
};